/*
 * %W% %E%
 *
 * Copyright 1997, 1998 Sun Microsystems, Inc. All Rights Reserved.
 *
 * Redistribution and use in source and binary forms, with or
 * without modification, are permitted provided that the following
 * conditions are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 *
 * - Redistribution in binary form must reproduce the above
 *   copyright notice, this list of conditions and the following
 *   disclaimer in the documentation and/or other materials
 *   provided with the distribution.
 *
 * Neither the name of Sun Microsystems, Inc. or the names of
 * contributors may be used to endorse or promote products derived
 * from this software without specific prior written permission.
 *
 * This software is provided "AS IS," without a warranty of any
 * kind. ALL EXPRESS OR IMPLIED CONDITIONS, REPRESENTATIONS AND
 * WARRANTIES, INCLUDING ANY IMPLIED WARRANTY OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT, ARE HEREBY
 * EXCLUDED. SUN AND ITS LICENSORS SHALL NOT BE LIABLE FOR ANY
 * DAMAGES OR LIABILITIES SUFFERED BY LICENSEE AS A RESULT OF OR
 * RELATING TO USE, MODIFICATION OR DISTRIBUTION OF THIS SOFTWARE OR
 * ITS DERIVATIVES. IN NO EVENT WILL SUN OR ITS LICENSORS BE LIABLE
 * FOR ANY LOST REVENUE, PROFIT OR DATA, OR FOR DIRECT, INDIRECT,
 * SPECIAL, CONSEQUENTIAL, INCIDENTAL OR PUNITIVE DAMAGES, HOWEVER
 * CAUSED AND REGARDLESS OF THE THEORY OF LIABILITY, ARISING OUT OF
 * THE USE OF OR INABILITY TO USE THIS SOFTWARE, EVEN IF SUN HAS
 * BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
 *
 * You acknowledge that this software is not designed, licensed or
 * intended for use in the design, construction, operation or
 * maintenance of any nuclear facility.
 */
package edu.unc.its.tl.bb;


/**
 * An implementation of MergeSort, needs to be subclassed to provide a
 * comparator.
 *
 * @version %I% %G%
 *
 * @author Scott Violet
 */
public abstract class MergeSort extends Object {
   protected Object toSort[];
   protected Object swapSpace[];

   public void sort(Object[] array) {
      if (array != null && array.length > 1) {
         int maxLength;

         maxLength = array.length;
         swapSpace = new Object[maxLength];
         toSort = array;
         this.mergeSort(0, maxLength - 1);
         swapSpace = null;
         toSort = null;
      }
   }

   public abstract int compareElementsAt(int beginLoc, int endLoc);

   protected void mergeSort(int begin, int end) {
      if (begin != end) {
         int mid;

         mid = (begin + end) / 2;
         this.mergeSort(begin, mid);
         this.mergeSort(mid + 1, end);
         this.merge(begin, mid, end);
      }
   }

   protected void merge(int begin, int middle, int end) {
      int firstHalf, secondHalf, count;

      firstHalf = count = begin;
      secondHalf = middle + 1;
      while ((firstHalf <= middle) && (secondHalf <= end)) {
         if (this.compareElementsAt(secondHalf, firstHalf) < 0)
            swapSpace[count++] = toSort[secondHalf++];
         else
            swapSpace[count++] = toSort[firstHalf++];
      }
      if (firstHalf <= middle) {
         while (firstHalf <= middle)
            swapSpace[count++] = toSort[firstHalf++];
      } else {
         while (secondHalf <= end)
            swapSpace[count++] = toSort[secondHalf++];
      }
      for (count = begin; count <= end; count++)
         toSort[count] = swapSpace[count];
   }
}

